In recent years, marine resource exploration equipments and undersea earthquake sensor networks for early earthquake detection are becoming widespread, and there is an increased demand for an apparatus for supplying electric power to these equipments. The apparatus for supplying electric power needs to use a wireless power transmission technique that enables efficient power transmission even in seawater, because the surrounding area of the apparatus is seawater. The wireless power transmission technique needs to be a technique that does not require the power supply metal plugs to be exposed, and that has no possibility of shorting even in seawater, which has an electric conductivity of approximately 4 S/m.
In general, a transmission apparatus that wirelessly transmits/receives electric power has a coil formed by a conductor wire wound thereon several times. Application of alternating current power to this coil produces a magnetic flux that interlinks with the coil. As a result of this magnetic flux interlinking with the coil of the receiving apparatus, induced current is generated in the coil of the receiving apparatus, and thereby power transmission is performed.
Regarding the wireless technique, for example, Patent Document 1 discloses a technique in which a terminal device main body and a removable electronic device such as a memory card, perform electromagnetic induction type communication using wireless millimeter wave signals.
Patent Document 2 discloses a technique that uses electromagnetic induction in which an inductance value between the transmission apparatus and the receiving apparatus is increased to thereby increase the distance of electric power transmission.
Patent Document 3 discloses a technique that uses electromagnetic induction in which resonance (magnetic field resonance) is made at the same frequency, using a coil of a high Q value, to thereby improve mutual inductance between the transmission apparatus and the receiving apparatus, and increase the distance of electric power transmission.